LCDs have a number of advantages, including their lighter weight, reduced thickness and smaller power dissipation, over other kinds of display devices, and have been used as not only a display device with a small screen such as the monitor of a cellphone but also the big screen of a TV set. Recently, as there is an increasing demand for driving a liquid crystal display device at even higher rates, someone proposed a driving method, in which according to a combination of the grayscale levels of an input video signal in one and the previous vertical scanning periods, a different effective voltage from the one corresponding to the grayscale level in the former vertical scanning period is applied (see Patent Document No. 1, for example). Such a driving method is sometimes called an “overdrive driving”, by which the display quality can be improved when the grayscale level of an input video signal changes.
Meanwhile, liquid crystal display devices that add four or more primary colors together have recently been proposed as a replacement for an ordinary liquid crystal display device that uses the three primary colors. A liquid crystal display device of the former type is sometimes called a “multi-primary-color liquid crystal display device”. In general, a multi-primary-color liquid crystal display device uses not only the three primary colors (namely, red, green and blue) but also another primary color as well, and attempts to expand the color reproduction range. Also, a multi-primary-color liquid crystal display device performs a display operation by converting the grayscale levels of an input video signal that can be displayed by a normal three-primary-color display device into those corresponding to four or more primary colors (see Patent Documents Nos. 2 and 3). And such a conversion is called a “multi-primary-color conversion”.